1. Field of the Invention
The present invention relates to a position indicating device which allows the position of an object, along a secondary axis, to be detected while the object is being scanned in a primary axis. In particular, the invention relates to an apparatus wherein a scanning array which is used to detect the profile of an object in a primary axis is also used to detect position of the object in a secondary axis.
2. Description of the Related Art
There are many applications for which it is desirable to scan an object in order to obtain a positional profile of the object. For example, conventional sawmill devices utilize a photocell array to determine the profile of a log to cut the log in a manner that maximizes yield. In particular, an array of transmitters, such as photo-emitter devices is aligned in parallel with a transverse axis of a rotary saw blade and an array of receivers, such as photo-detectors, are aligned in opposition to the transmitter array. In this manner, the two arrays define a plurality of transmitter/receiver pairs that can each detect the presence/absence of a portion of the log therebetween. Therefore, the status of the receivers taken in combination is indicative of the profile of the log.
In such a conventional device, the log is supported on a moveable carriage in order to allow the log to be fed along the primary axis to a position in front of the blade. The carriage is also moveable along a secondary axis toward the blade to accomplish a cutting operation. Of course in order to obtain meaningful profile data, the position of the log along the secondary axis must be determined in a precise manner. Known systems accomplish this by detecting the position of the carriage, upon which the log is supported, through the use of an encoder device coupled the carriage or the drive mechanism associated with the carriage.
Encoders, such as an optical encoder using and encoded wheel must be precisely calibrated. Also, known encoders are fragile and expensive. Further, since an encoder must be mechanically coupled to the carriage or drive device, mechanical tolerance must be very precise in order to obtain a reliable portion signal. This further complicates the structure and raises the cost of conventional positioning devices.